First documented record of cookie-cutter shark (Isistius spp.) bite marks on a killer whale (Orcinus orca) in the Southwestern Atlantic Ocean

Abstract

Cookiecutter sharks (Isistius spp.) are small pelagic predators known for their specialized "plug-feeding" strategy, which leaves distinctive oval-to-elliptical wounds on diverse marine vertebrates. While these interspecific interactions are well-documented globally, records involving killer whales (Orcinus orca) in the Southwestern Atlantic remain scarce. This study documents skin lesions consistent with Isistius spp. predation on an adult male killer whale (6.5 m) that died during a mass stranding event on September 16, 2019, at La Caleta, Buenos Aires Province, Argentina (37°46´ S).Using standardized diagnostic criteria, a qualitative analysis of photographic evidence revealed multiple lesions across the cephalic, lateral, and ventral regions. The wounds, measuring between 4 and 6 cm in diameter, displayed varying stages of healing, from active crater wounds to depressed scars. These findings are morphologically and metrically consistent with the feeding marks of I. brasiliensis or I. plutodus. Representing one of the southernmost records of such interactions in the Southwestern Atlantic (37°47´ S), this report provides the first documentation of Isistius spp. bite marks on a large delphinid in Argentine temperate waters. These results expand the known host range for the genus and provide essential baseline data for future studies on cetacean health and interspecific interactions in the region.